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Chapter 11

Chapter 11. Lower End Theory and Service. Engine Lower End. The lower end of an engine is the cylinder block assembly Includes the block, crankshaft, bearings, pistons, connecting rods, oil pump, and camshaft on OHV designs This assembly is called a short block

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Chapter 11

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  1. Chapter 11 Lower End Theory and Service

  2. Engine Lower End • The lower end of an engine is the cylinder block assembly • Includes the block, crankshaft, bearings, pistons, connecting rods, oil pump, and camshaft on OHV designs • This assembly is called a short block • A short block plus the cylinder head(s) is called a long block

  3. Lower End

  4. Short Block Disassembly • Remove oil pan and water pump • Remove the harmonic balancer • On OHV engines remove the timing cover • Inspect the timing chain and remove • Remove the oil pick up and oil pump • Remove lifters and keep them in order

  5. Cylinder Block Disassembly • Check balance shaft clearances if necessary and remove • Rotate crankshaft so cylinder #1 is at BDC • Carefully remove all cylinder ring ridges

  6. Cylinder Block Disassembly • Check bearing cap positions and mark if necessary

  7. Cylinder Block Disassembly (Cont.) • Position piston at BDC for removal • Remove connecting rod cap and cover rod bolts to prevent cylinder damage • Carefully push the piston and rod with wooden handle • Be sure connecting rod does not damage the cylinder wall

  8. Cylinder Block Disassembly (Cont.) • Remove the main bearing caps in the specified order • Some engines use a main bearing girdle or bedplate that houses the bearings • Carefully remove crank and store vertically • Remove the rear main oil seal and bearing inserts

  9. Cylinder Block Disassembly (Cont.) • Remove the block core plugs and oil plugs to ensure thorough cleaning Oil gallery plugs

  10. Cylinder Block • Houses areas where combustion takes place • Can be cast iron, aluminum or magnesium • Cast iron is very strong but heavy

  11. Cylinder Block (Cont.) • Most aluminum blocks use cylinder liners • Usually cannot be machined

  12. Cylinder Block (Cont.) • Oil and coolant passages within the block allow for the flow of oil and coolant

  13. Block Reconditioning • Inspect the block for cracks and damage • Clean all threaded bores with a thread chaser • Bolt holes should be slightly chamfered

  14. Block Reconditioning (Cont.) • Aluminum blocks with damaged threads may require a threaded insert – called a Helicoil

  15. Block Reconditioning (Cont.) • Deck flatness is important for proper cylinder head and intake manifold fit

  16. Block Reconditioning (Cont.) • Inspect cylinder walls • Wall scoring or scuffing • Most wear is at top of cylinder • Measure taper and out-of-roundness

  17. Cylinder Bore Finish • Surface finish must act as an oil reservoir • Rings can be damaged by a rough surface • Too smooth will not hold enough oil • Desired finish is a crisscross pattern

  18. Cylinder Bore Finish (Cont.) • Deglaze if cylinder condition is within specifications • Honing removes a small amount of metal from the cylinder walls • Boring is performed when the cylinder walls are worn excessively • Oversized pistons and rings are used after boring

  19. Knowledge Check • What may result if the cylinder bore finish is too smooth?

  20. Lifter Bores • Inspect bores for cracks and excessive wear • Can be honed with a wheel cylinder hone • If the lifter bores exceed allowable wear, the block should be replaced

  21. Crankshaft Saddle Alignment • Misalignment will cause the crankshaft to bend as it rotates • May be repaired by line boring • Badly warped blocks are replaced • Checked along the crankshaft saddle bore • Roundness should be checked as well

  22. Crankshaft Saddle Alignment

  23. Installing Core Plugs • After cleaning, the block should have new core and oil plugs installed • Coat the plug or bore lightly with a non-hardening sealer

  24. Camshafts • Have a cam lobe for each exhaust and intake valve • Lobe height is proportional to valve lift • May drive distributor and/or oil pump • May be iron, steel, or hollow

  25. OHV Camshafts • Works with lifters, pushrods, and rocker arms to open the valves

  26. Camshaft in Block

  27. OHC Camshafts • May be single or dual overhead camshafts • Can open valves directly or through lifters, followers, or rocker arms

  28. Camshafts (Cont.) • Driven at half of crankshaft speed • Cam gears are twice the size of crank gears • Each intake and exhaust valve opens and closes once per crankshaft rotation • Valve opening and closing based on the shape of the cam lobe

  29. Camshaft Terminology • The shape of the cam lobe is called the cam profile • Duration is the time the valve is open • Overlap is the time both the exhaust and intake valves are open at the same time

  30. Lobe Terminology

  31. Camshaft Drives • Belt Drive • Sprockets on the crankshaft and the camshaft are linked by a neoprene belt

  32. Camshaft Drives • Chain Drive • Sprockets on the crankshaft and the camshaft are linked by a continuous chain

  33. Camshaft Drives • Gear Drive • A gear on the crankshaft meshes directly with a gear on the camshaft

  34. Camshaft Drives (Cont.) • Tensioners may be spring loaded and/or hydraulically operated • Maintains correct belt or chain tension • Have a drive side and a slack side • The tensioner is on the slack side

  35. Variable Valve Timing (VVT) • VVT used on OHC and OHV engine designs • VVT systems use special camshafts and phasers

  36. Knowledge Check • What are the three types of camshaft drives?

  37. Lifter Types - Hydraulic Lifter • Hydraulic Lifters • Uses oil to absorb the shock from the valve train movement

  38. Lifter Types - Solid Lifter • Solid Lifters • Require a clearance between parts of the valve train

  39. Lifter Types - Roller Lifter • Roller Lifters • Uses a roller to minimize friction

  40. Camshaft Bearings • OHV engines are one piece bearings pressed into the camshaft bore • OHC can be supported by split bearings

  41. Balance Shafts • Balance or silence shafts are used to reduce engine vibration • Counterweights mirror the throws of the crankshaft • Rotate opposite crankshaft rotation • Inspected and serviced as part of engine reconditioning

  42. Balance Shaft (Cont.)

  43. Crankshafts • Made of iron or steel • Crankshaft main and rod journals are machined to very close tolerances • This allows an oil film between the journal and the bearing

  44. Crankshaft Torsional Dampers • Crankshaft twists and bends under combustion forces causing harmonic vibrations • This vibration can damage the crankshaft, the engine, and/or accessories driven by the crankshaft • Two common types of torsional dampers used

  45. Harmonic Balancer • Also called a vibration dampener • Composed of an inner hub and outer inertia ring connected via a rubber sleeve • As the crank twists the hub applies force to the ring • The condition of the sleeve is critical

  46. Harmonic Balancer

  47. Fluid Damper • Commonly installed by the aftermarket • Fluid filled dampers have a hub surrounded by the inertia ring • The ring is filled with a high viscosity fluid • The outer ring moves against the hub as it absorbs vibrations • This movement results in heat

  48. Flywheel • Helps the engine run smoother • Applies a constantly moving force to the crankshaft • Flywheel inertia helps keep the crank moving from one firing event to the next • On automatic transmissions, the flex-plate and torque converter act as a flywheel

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